This invention relates generally to electrostatic transducers such as loudspeakers, and more particularly concerns substantial improvements in the construction, mode of operation and performance of such speakers.
Various forms of electrostatic loudspeakers have been proposed for many years and in some instances have been commercially marketed. Perhaps the most familiar of the commercially available electrostatic loudspeakers is that developed by A. A. Janszen described in U.S. Pat. No. 2,631,196 and in U.S. Pat. No. 2,896,025. The Janszen speaker comprises an arrangement in which a flexible diaphragm or membrane is mounted between fixed electrodes in the form of a grid of wires. The wires are spaced apart so as to enable sound waves generated by movement of the flexible diaphragm to be emitted. The wires are sheathed in a dielectric insulation material and the flexible membrane bears a coating of a highly resistive material. By means of an open latticed frame, the membrane is suspended between the electrode wires and clamped in position by dividers of the lattice so that in operation relatively small segments of the diaphragm are enabled to vibrate under the influence of electrostatic fields acting upon the diaphragm.
The Janszen speaker and other known electrostatic speakers require the application of a relatively high polarizing voltage between the flexible diaphragm and the wire grid electrodes for their operation. In order to operate with a constant charge they additionally require a relatively high series resistor between the source of polarizing voltage and the electrodes. Due to the configuration of the known speakers the electrical capacity is relatively low, and due to the presence of the highly resistive coating on the flexible diaphragm they possess a relatively low efficiency in converting applied electrical signals to audible sound waves. However, perhaps the most serious deficiency of the Janszen speakers and all other previously known electrostatic speakers either proposed or commercially available is that their characteristics of relatively low capacity, relatively low efficiency, mechanical size and configuration, relatively small segments of vibrating diaphragm area and resistive coatings lead to an inability to adequately reproduce relatively low sound frequencies. Accordingly, in most instances known electrostatic speakers have been used to reproduce only the mid-range and higher audible frequencies requiring that they be employed in conjunction with a base frequency speaker sometimes known as a "woofer."
Other examples of electrostatic speakers in the prior art may be found in the patents of D. T. N. Williamson et al U.S. Pat. Nos. 3,008,013 and 3,008,014, Malme U.S. Pat. No. 3,014,098 and an article entitled "Electrostatic Speakers" by George W. Tillet appearing in "Audio Magazine" for March of 1971 at page 52 et seq. and an article by P. J. Walker appearing in parts in "Wireless World" for May, June and August of 1955. However, none of the known prior art speakers possess the advantages and improved operating characteristics of the present invention.